4-stator-pole step motor with passive inter-poles

Abstract

A two-phase bipolar step motor, comprises a rotor having a plurality of pairs of rotor poles of alternating magnetic polarity, and a stator having four primary energizable stator poles with conductive windings around those primary stator poles and four passive inter-poles located uniformly between every adjacent pair of primary stator poles, the passive inter-poles lacking any conductive windings. Both 18° steppers with five pairs of rotor poles and 30° steppers with three pairs of rotor poles are provided. Also provided are both PM hybrid mix steppers with 2D magnetic flux paths and hybrid steppers with 3D magnetic flux paths having an axial component. In each case, the overall lengths of the flux paths are substantially reduced from conventional designs resulting in improved motor efficiency.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application claims priority under 35 U.S.C. 119(e) from U.S. Provisional Application 63 / 138,150, filed Jan. 15, 2021.TECHNICAL FIELD[0002]The invention relates generally to motors wherein a rotor driven by a stator rotates step-by-step between successive detent positions, i.e., stepping motors, and more specifically to stepping motors with a four-stator-pole design with large fundamental step angles, such as 18° and 30° steppers, with particular emphasis on increasing motor efficiency.BACKGROUND ART[0003]A wide range of motor applications, including the orienting of communication devices, surveillance cameras, and stage lighting, need only relatively low directional resolution, but require adequate dynamic and holding torque from the motors to be able to reorient such equipment at a useful speed. 18° permanent magnet (PM) type stepping motors are frequently used for this purpose because of their speed and torque performance. However, ...

AI Technical Summary

Benefits of technology

[0008]A two-phase bipolar step motor is provided that significantly shortens the magnetic flux paths in all drive phases by providing four dummy inter-poles in addition to the four primary energizable stator poles. The motor includes a rotor having a plurality of rotor poles in pairs of alternating N and S magnetic polarity. The stator has four primary stator poles terminating at their innermost ends in stator shoes and with conductive windings around those stator poles, and four dummy inter-poles located uniformly between every adjacent pair of primary stator poles. The dummy inter-poles lack any conductive windings and typically lack pole shoes. Both the primary stator poles and the dummy inter-poles are radially spaced from the rotor by a narrow air gap that is identical for all primary stator poles and dummy inter-poles. The four dummy inter-poles may have a circumferential dimension or arcuate width that is a factor in a range from 0.6 to 0.8 of a circumferential dimension of the four primary stator poles. The magnetic flux paths created by the primary energized stator poles pass from those stator poles to return through adjacent dummy inter-poles creating much shorter paths than the conventional design.

[0009]Two typical examples are an 18° stepper and a 30° stepper. They both have four primary energizable stator poles and have improved performance with the addition of the four dummy inter-poles. In the 18° stepper, there are five pairs of N and S rotor poles with a rotor tooth pitch of 72°. The motor is characterized by a full step of 18° between successive one-phase ON detent positions and by a half step of 9° between one-phase ON and two-phase ON detent positions. In the 30° stepper, there are three pairs of N and S rotor poles with a rotor tooth pitch of 120°. The motor is characterized by a full step of 30° between successive one-phase ON detent positions and by a half step of 15° between one-phase ON and two-phase ON detent positions.

[0011]Adding the four inter-poles between the four primary energizable stator poles will shorten the flux paths both in the one-phase ON and two-phase ON drive conditions relative to the prior conventional design, improving motor efficiency. Additionally, the use of the inter-poles will minimize flux leakage in the hybrid PM mix steppers. The invention fully utilizes the magnetic flux on the rotor to develop maximum torque.

Problems solved by technology

The dummy inter-poles lack any conductive windings and typically lack pole shoes.

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